Exploring the effects of cochineal and indigotin extracts on the properties of plasma electrolytic oxidation coating

Abstract

The aim of this study is to investigate the effectiveness of chromophoric organic compounds in modifying the surface of AZ31 Mg alloy using the plasma electrolytic oxidation (PEO) process. In particular, the study examines the deposition of cochineal extract and indigotin extract on PEO coatings and evaluates their impact on the morphology, structure, and properties of the resulting coatings. The PEO coatings were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD), while the anti-corrosive properties were characterized by potentiodynamic polarization (POL) measurements. The results indicate that the deposition of chromophores of cochineal extract on PEO coatings leads to a smoother surface morphology, while indigotin deposition results in a partially sealed surface with large cracks. The combined solution of both the organic extracts results in a higher carbon content but does not effectively seal the surface, likely due to the formation of larger molecules that cannot fully penetrate the pores of the PEO coating. Overall, this study demonstrates the potential of chromophoric organic compounds for surface modification of Mg alloys and highlights the importance of careful selection and characterization of the post-treatment compounds.